It’s the Vehicle Assembly Building

The VAB covers 3.25 hectares (8 acres). It is 160 meters (525 ft) tall, 218 meters (716 ft) long and 158 meters (518 ft) wide. It encloses 3,664,883 cubic meters (129,428,000 cubic feet) of space.

Flag & Bicentennial Emblem: Added in 1976, required 6,000 gallons of paint. The flag is 64 x 33.5 meters (209 x 110 ft) in size. Each strip on the flag is as big as the tour buses used to transport visitors around KSC
Steel: 89,421 metric tons (98,590 tons)
Concrete: 49,696 cubic meters (65,000 cubic yards)
Piling: 4,225 open-end steel pipe piles, 0.4 meters (16 inchs) in diameter were driven 49 meters (160 ft) into bedrock.
Air Conditioning: 9,070 metric tons (10,000 tons), 125 ventilators.
Lifting Devices: 71 cranes; two 227 metric ton (250 ton) bridge cranes.
Siding: 100,800 sq meters (1,085,000 sq ft) insulated aluminum panels; 6,503 sq meters (70,000 sq ft) plastic panels.
Doors: There are 4 High Bay doors. Each opening is 139 meters (456 ft) high. The north entry to the transfer aisle was widened 12.2 meters (40ft) to permit entry of the Orbiter, and slotted at the center to accommodate its vertical stabilizer.

Both previous respondents got the height correct. I do want to add that very early on, the term Vertical Assembly Building was, indeed used, but I think the term Vehicle Assembly Building has always been the official name. When it was first constructed it was the largest building in the world, in terms of volume. It is so large that (it’s said) it sometimes rains inside.